1. Field of Invention
The present invention relates to a recording material for back-printing that is suitable as an illuminated film for ink jet recording or the like.
2. Description of Related Art
As shown in FIG. 2, a back-printing sheet 20 generally has a layered structure in which a transparent substrate 21 of PET or the like, an ink-absorbing layer 22, and a porous white ink-receiving layer 23 that has filler, i.e., a light-diffusing substance, dispersed in a binder resin are built up in this order. Here, the ink-absorbing layer 22 has better ink holding ability than the ink-receiving layer 23. Moreover, with such a back-printing sheet 20, an ink image is formed using an ink jet printer or the like on the surface of the ink-receiving layer 23, and this ink image permeates through the ink-receiving layer 23 and is held by the ink-absorbing layer 22. The ink image held by the ink-absorbing layer 22 is viewed from the transparent substrate 21 side.
An example of a usage of such a back-printing sheet 20 is a usage as an illuminated film. In this usage, light from a light source (backlight) positioned behind (i.e. on the ink-receiving layer side of) the back-printing sheet, which has had an ink image formed thereon, is irradiated onto the back-printing sheet, and the ink image is viewed from the transparent substrate 21 side.
Recently it has become common to put up illuminated films outdoors, and hence the ink-receiving layer 23 on which the ink image is formed in the back-printing sheet 20 is required to have better water resistance, gas degradation resistance, light resistance and so on than that previously required. A cover film, in which an adhesive layer comprising an acrylic adhesive resin or the like is formed on a polyester substrate, may thus be stuck onto the ink-receiving layer 23 on which the ink image has been formed.
However, in the case that a back-printing sheet on which an ink image has been formed has been put up outdoors as an illuminated film for a prolonged time, even though a cover film has been stuck onto the ink-receiving layer, there has still been a problem that the level of light diffusion at filler surfaces drops, and hence the ink-receiving layer 23 becomes transparent.